Olefin oligomers and relatively long chain olefins can be used in the production of fuel and lubricant components or blendstocks. One problem with the use of olefin oligomers in either of the above uses is that the olefinic double bond can be undesirable. Olefinic double bonds cause problems in both fuels and in lubricants. Olefin oligomers can further oligomerize forming ‘gum’ deposits in the fuel. Olefins in fuel are also associated with air quality problems. Olefins can also oxidize which can be a particular problem in lubricants. One way of minimizing the problem is to hydrogenate some or all of the double bonds to form saturated hydrocarbons. A method of doing this is described in US published Application US 2001/0001804 which is incorporated herein in its entirety. Hydrogenation can be an effective way to minimize the concentration of olefins in the lubricant or fuel however it requires the presence of hydrogen and a hydrogenation catalyst both of which can be expensive. Also excessive hydrogenation can lead to hydrocracking. Hydrocracking can increase as one attempts to hydrogenate the olefins to increasingly lower concentrations. Hydrocracking is generally undesirable as it produces a lower molecular weight material where the goal in oligomerization is to produce a higher molecular weight material. Directionally it would generally be preferred to increase, not decrease the average molecular weight of the material. Thus using the hydrogenation method it is desired to hydrogenate the olefins as deeply as possible while minimizing any hydrocracking or hydrodealkylation. This is inherently difficult and tends to be a compromise.
Hydrocracking of a slightly branched hydrocarbon material can also lead to less branching. Cracking tend to be favored at the tertiary and secondary centers. For example a branched hydrocarbon can crack at a secondary center forming two more linear molecules which is also directionally undesirable.
Potentially, Ionic Liquid catalyst systems can be used for the oligomerization of olefins such as normal alpha olefins to make olefin oligomers. A patent that describes the use of an ionic liquid catalyst to make polyalphaolefins is U.S. Pat. No. 6,395,948 which is incorporated herein by reference in its entirety. A published application that discloses a process for oligomerization of alpha olefins in ionic liquids is EP 791,643.
Ionic Liquid catalyst systems have also been used for isoparaffins-olefins alkylation reactions. Patents that disclose a process for the alkylation of isoparaffins by olefins are U.S. Pat. No. 5,750,455 and U.S. Pat. No. 6,028,024.
It would be desirable to have a process for making a lubricant or distillate fuel starting materials with low degree of unsaturation (low concentration of double bonds) and thus reducing the need for exhaustive hydrogenation while preferably maintaining or more preferably increasing the average molecular weight and branching of the material. The present invention provides a new process with just such desired features.